We understand what happens outside the black hole as you approach its event horizon, that infamous point of no return. The event horizon is where the escape speed exceeds the speed of light: you’d have to be going faster than light (which is impossible for any bit of matter) to escape the black hole’s gravity. Inside the event horizon is where physics goes crazy. Calculations suggest that what the fabric of spacetime looks like inside a black hole depends on that particular black hole’s history. It might be turbulent, twisted, or any other number of things. One thing’s for sure, though: the tidal forces would kill you (see below). According to theory, within a black hole there’s something called a singularity. A singularity is what all the matter in a black hole gets crushed into. Some people talk about it as a point of infinite density at the center of the black hole, but that’s probably wrong — true, it’s what classical physics tells us is there, but the singularity is also where classical physics breaks down, so we shouldn’t trust what it says here. In a very specific mathematical case, the singularity in a spinning black hole becomes a ring, not a point. But that mathematical situation won’t exist in reality. Others say that the singularity is actually a whole surface inside the event horizon. We just don’t know. It could be that, in real black holes, singularities don’t even exist.
